pull up r18754 from trunk

pull up r18754 from trunk

 r18754@cathode-dark-space:  coffman | 2006-11-01 17:40:30 -0500
 ticket: 4566
 ticket: 4567
 ticket: 4587
 Target_Version: 1.6
 Tags: pullup

 Modify the preath plugin interface so that a plugin's context is
 global to all the modules within a plugin.  Also, change the
 client-side interface so that the preauth plugin context (once
 created) lives the lifetime of a krb5_context.  This will allow
 future changes that can set plugin parameters.  The client side
 request context lives the lifetime of a call to krb5_get_init_creds().

 Make the sample preauth plugins buildable outside the source tree.

 Fix minor memory leak in sort_krb5_padata_sequence().

 Add a prototype for krb5_do_preauth_tryagain() and change the plugin
 interface.

 Incorporates fixes from Nalin Dahyabhai <nalin@redhat.com> for leaks
 of the function table pointers (rt #4566) and fix KDC crash (rt #4567)

ticket: 4566
ticket: 4567
ticket: 4587
version_fixed: 1.6

git-svn-id: svn://anonsvn.mit.edu/krb5/branches/krb5-1-6@18777 dc483132-0cff-0310-8789-dd5450dbe970